Coronary Heart Disease is the leading cause of death in our society. Underlying this disease is the pathologic process known as atherosclerosis. The central theme of this Program is to define aspects of lipoprotein metabolism important in atherogenesis. Atherosclerosis occurs when plasma low density lipoproteins (LDL) get deposited in the artery wall. Atherosclerotic lesions rich in cholesteryl esters develop in response to LDL deposition. Studies in this program project will help define how LDL precursor lipoproteins are actually made inside cells (Project 2), how concentrations are controlled, and properties of LDL that make them more atherogenic. We have identified an enzyme in the liver and intestine, termed ACAT2, that appears to be important in this context, and we will use genetically engineered mice that no longer have this enzyme to show how this enzyme alters cholesterol metabolism in the liver and in the intestine (Project 1). We will test the hypothesis that cholesteryl oleate accumulation in plasma as LDL promotes atherosclerosis, and we will attempt studies to determine if we can identify cholesteryl oleate as a biomarker for ACAT2 in humans. High density lipoproteins (HDL) are the class of lipoproteins that help remove cholesterol from arteries. We will do studies to help determine how HDL particles are made. We know that the principal protein of HDL, called apoA-l, is secreted without lipid into plasma and then assembles lipid after interaction on the surface of cells with a transporter termed ABCA1 found mostly in the liver. Factors influencing this interaction will be measured (Project 3). Further, the properties of the major protein of HDL, termed apoA-l, which are responsible for its efficient function in lipid assimilation and transport will be assessed in Project 4. Important characteristics of the protein will be identified through the study of natural mutations of the protein using techniques to define protein structure. In all of these projects, genetically engineered mice will provide specific insights into molecular physiology. Overall, this program project will provide basic information that will help us understand the role of lipoprotein metabolism in atherosclerosis so that prevention of CHD can be more readily achieved.